1. Technical Field
The present invention relates to a method for reducing the amount of asparagine, a pre-cursor of acrylamide in a food product. This invention permits the production of foods having significantly reduced levels of acrylamide, and more particularly the invention is directed towards a method for leaching at least one acrylamide pre-cursor with an extract that is deficient in the acrylamide pre-cursor being leached.
2. Description of Related Art
The chemical acrylamide has long been used in its polymer form in industrial applications for water treatment, enhanced oil recovery, papermaking, flocculants, thickeners, ore processing and permanent-press fabrics. Acrylamide precipitates as a white crystalline solid, is odorless, and is highly soluble in water (2155 g/L at 30° C.). Synonyms for acrylamide include 2-propenamide, ethylene carboxamide, acrylic acid amide, vinyl amide, and propenoic acid amide. Acrylamide has a molecular mass of 71.08, a melting point of 84.5° C., and a boiling point of 125° C. at 25 mmHg.
In very recent times, a wide variety of foods have tested positive for the presence of acrylamide monomer. Acrylamide has especially been found primarily in carbohydrate food products that have been heated or processed at high temperatures. Examples of foods that have tested positive for acrylamide include coffee, cereals, cookies, potato chips, crackers, french-fried potatoes, breads and rolls, and fried breaded meats. In general, relatively low contents of acrylamide have been found in heated protein-rich foods, while relatively high contents of acrylamide have been found in carbohydrate-rich foods, compared to non-detectable levels in unheated and boiled foods. Reported levels of acrylamide found in various similarly processed foods include a range of 330-2,300 (μg/kg) in potato chips, a range of 300-1100 (μg/kg) in French fries, a range 120-180 (μg/kg) in corn chips, and levels ranging from not detectable up to 1400 (μg/kg) in various breakfast cereals.
It is presently believed that acrylamide is formed from the presence of amino acids and reducing sugars. For example, it is believed that a reaction between free asparagine, an amino acid commonly found in raw vegetables, and free reducing sugars accounts for the majority of acrylamide found in fried food products. Asparagine accounts for approximately 40% of the total free amino acids found in raw potatoes, approximately 18% of the total free amino acids found in high protein rye, and approximately 14% of the total free amino acids found in wheat.
The formation of acrylamide from amino acids other than asparagine is possible, but it has not yet been confirmed to any degree of certainty. For example, some acrylamide formation has been reported from testing glutamine, methionine, cysteine, and aspartic acid as pre-cursors. These findings are difficult to confirm, however, due to potential asparagine impurities in stock amino acids. Nonetheless, asparagine has been identified as the amino acid pre-cursor most responsible for the formation of acrylamide.
Since acrylamide in foods is a recently discovered phenomenon, its exact mechanism of formation has not been confirmed. However, it is now believed that the most likely route for acrylamide formation involves a Maillard reaction. The Maillard reaction has long been recognized in food chemistry as one of the most important chemical reactions in food processing and can affect flavor, color, and the nutritional value of the food. The Maillard reaction requires heat, moisture, reducing sugars, and amino acids.
The Maillard reaction involves a series of complex reactions with numerous intermediates, but can be generally described as involving three steps. The first step of the Maillard reaction involves the combination of a free amino group (from free amino acids and/or proteins) with a reducing sugar (such as glucose) to form Amadori or Heyns rearrangement products. The second step involves degradation of the Amadori or Heyns rearrangement products via different alternative routes involving deoxyosones, fission, or Strecker degradation. A complex series of reactions including dehydration, elimination, cyclization, fission, and fragmentation result in a pool of flavor intermediates and flavor compounds. The third step of the Maillard reaction is characterized by the formation of brown nitrogenous polymers and co-polymers. Using the Maillard reaction as the likely route for the formation of acrylamide, FIG. 1 illustrates a simplification of suspected pathways for the formation of acrylamide starting with asparagine and glucose.
Acrylamide has not been determined to be detrimental to humans, but its presence in food products, especially at elevated levels, is undesirable. As noted previously, relatively higher concentrations of acrylamide are found in food products that have been heated or thermally processed. The reduction of acrylamide in such food products could be accomplished by reducing or eliminating the precursor compounds that form acrylamide, inhibiting the formation of acrylamide during the processing of the food, breaking down or reacting the acrylamide monomer once formed in the food, or removing acrylamide from the product prior to consumption. Understandably, each food product presents unique challenges for accomplishing any of the above options. For example, foods that are sliced and cooked as coherent pieces may not be readily mixed with various additives without physically destroying the cell structures that give the food products their unique characteristics upon cooking. Other processing requirements for specific food products may likewise make acrylamide reduction strategies incompatible or extremely difficult.
By way of example, FIG. 2 illustrates well known prior art methods for making fried potato chips from raw potato stock. The raw potatoes, which contain about 80% or more water by weight, first proceed to a peeling step 21. After the skins are peeled from the raw potatoes, the potatoes are then transported to a slicing step 22. The thickness of each potato slice at the slicing step 22 is dependent on the desired the thickness of the final product. An example in the prior art involves slicing the potatoes to a thickness of about 0.04 to about 0.08 inches. These slices are then transported to a washing step 23, wherein the surface starch on each slice is removed with water. The washed potato slices are then transported to a cooking step 24. This cooking step 24 typically involves frying the slices in a continuous fryer at, for example, about 171° C. to about 182° C. (340-360° F.) for approximately two to three minutes. The cooking step generally reduces the moisture level of the chip to less than 2% by weight. For example, a typical fried potato chip exits the fryer with approximately 1-2% moisture by weight. The cooked potato chips are then transported to a seasoning step 25, where seasonings are applied in a rotation drum. Finally, the seasoned chips proceed to a packaging step 26. This packaging step 26 usually involves feeding the seasoned chips to one or more weighers which then direct chips to one or more vertical form, fill, and seal machines for packaging in a flexible package. Once packaged, the product goes into distribution and is purchased by a consumer.
Minor adjustments in a number of the potato chip processing steps described above can result in significant changes in the characteristics of the final product. For example, an extended residence time of the slices in water at the washing step 23 can result in leaching compounds from the slices that provide the end product with its potato flavor, color and texture. Increased residence times or heating temperatures at the cooking step 24 can result in an increase to in the Maillard browning levels in the chip, as well as a lower moisture content. If it is desirable to incorporate ingredients into the potato slices prior to frying, it may be necessary to establish mechanisms that provide for the absorption of the added ingredients into the interior portions of the slices without disrupting the cellular structure of the chip or leaching beneficial compounds from the slice.
By way of another example of heated food products that represent unique challenges to reducing acrylamide levels in the final products, snacks can also be made as a fabricated snack. The term “fabricated snack” means a snack food that uses as its starting ingredient something other than the original and unaltered starchy starting material. For example, fabricated snacks include fabricated potato chips that use a dehydrated potato product as a starting material and corn chips which use a masa flour as its starting material. It is noted here that the dehydrated potato product can be potato flour, potato flakes, potato granules, or any other form in which dehydrated potatoes exist. When any of these terms are used in this application, it is understood that all of these variations are included.
Referring back to FIG. 2, a fabricated potato chip does not require the peeling step 21, the slicing step 22, or the washing step 23. Instead, fabricated potato chips start with a dehydrated potato product such as potato flakes. The dehydrated potato product is mixed with water and other minor ingredients to form a dough. This dough is then sheeted and cut before proceeding to a cooking step. The cooking step may involve frying or baking. The chips then proceed to a seasoning step and a packaging step. The mixing of the potato dough generally lends itself to the easy addition of other ingredients. Conversely, the addition of such ingredients to a raw food product, such as potato slices, requires that a mechanism be found to allow for the penetration of ingredients into the cellular structure of the product. However, the addition of any ingredients in the mixing step must be done with the consideration that the ingredients may adversely affect the sheeting characteristics of the dough as well as the final chip characteristics.
It would be desirable to develop one or more methods of reducing the level of acrylamide in the end product of heated or thermally processed foods. Ideally, such a process should substantially reduce or eliminate the acrylamide in the end product without adversely affecting the quality and characteristics of the end product. Further, the method should be easy to implement and, preferably, add little or no cost to the overall process.
U.S. Pat. No. 3,934,046 (“Weaver”), does not specifically address a method for reducing acrylamide formation but, its teachings are pertinent to the problem at hand. It is well known in the art that the browning of thermally processed foods is caused in part by the heating of amino acids, such as asparagine, in the presence of reducing sugars. As explained in Weaver, “the browning tendency of the tubers increases as the content of reducing sugars increases. It has also been demonstrated that the reducing sugars react with the nitrogenous constituents in the potatoes, producing dark-colored reaction products.” Weaver teaches that leaching raw potato pieces with hot water reduces the browning that occurs in the cooking phase. Weaver, however, also explains the undesirable effect of leaching purely with hot water: “in the case of potato chips, hot-water leaching is not employed because texture and flavor are almost completely destroyed under conditions necessary to adequately prevent darkening.” This is because the water leaches all components of the potato slices for which a concentration gradient exists between the potato stock and the water. Consequently, all sugars and amino acids are leached indiscriminately from the potato stock.
Although Weaver was not directed towards reducing acrylamide levels in thermally processed foods, Weaver's general concept of leaching potato pieces can be improved upon and applied to the present problem of reducing acrylamide formation. It would therefore be useful to have a method for reducing acrylamide formation in thermally processed foods by leaching acrylamide pre-cursors selectively out of raw food pieces without substantially affecting food texture and flavor. Such a method would ideally require removing the leached acrylamide pre-cursors from the leaching extract in order to reuse the leaching extract.